Amrein, T. (Corresponding author)FZJ* ; Institut für Festkörperforschung (Jülich) ; Technische Hochschule (Aachen)

1994
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Report No.: Juel-2952

Abstract: A pulsed laser deposition process is developed for preparing high quality thin films of Bi2Sr2CaCu20x on different substrates. Both microstructural and electrical properties of the superconducting films are well characterized, e.g. by SEM, TEM and AFM. The high reproducability of the thin film quality facilitated a detailed study of Josephson effects in bicrystalline grain boundary junctions (OBJs). Thin films are deposited on commercially available (001) SrTi03 bicrystals and patterned by standard photolithography using wet-etching or Ar"-ion milling. The width of the micobridges ranges from 2 to 111 urn. The critical current densities across grain boundaries of thin film bicrystals have been measured as a function of the tilt angle e. For 8=0° to 45°, the ratio of the grain boundary critical current density to the bulk critical current density decreases exponentially with increasing tilt angle. Microstructure investigations show a rough grain boundary of the superconductor (roughness 100 nm - 1 urn) which is not determined by the roughness of the substrate grain boundary (1 - 3 nm) but by the island-pluslayer growth of the twin domains. The electrical properties are well described by the resistively shunted junction (RSJ) model. The !eRn-product reaches values of 2.2 mV at 4.2 K and 60 ""V at 77 K. An optimized design for dc SQUIDs (e=24°) is developed relating to the the results of single GBJs. The values of the transfer function (oV/oCP) run up to 74IlV/CPo. The equivalent flux noise which is measured in a flux-locked loop mode amounts 4.5 to 25 ""CPolJHz in the white noise region for f > 25-50 Hz and 13 to 150 ""CPo/1Hz at 1 Hz. In conclusion, microstructural as well as electrical properties of bicrystalline Bi2Sr2CaCu20x and YBa2CU30y GBls are more or less equal

Keyword(s): Josephson effect ; superconducting film ; high temperature superconductor

1. Institut für Festkörperforschung (IFF)